* {
  box-sizing: border-box;
}
body {
  background-color: skyblue;
  color: #fff;
  display: flex;
  flex-direction: column;  /* 改变子元素的排列方式 */
  justify-content: center;
  align-items: center;
  height: 100vh;
  margin: 0;
}
.container {
  background-image: linear-gradient(to bottom right, #ff9966, #ff5e62);
  padding: 20px 40px;
  /* width: 300px; */
  /* height: 300px; */
  /* max-height: 100vh; */
  border-radius: 10px;
}
.container h1 {
  text-align: center;
  margin-bottom: 30px;
}
.container form .form-control{
  /* display: flex; */
  position: relative;
  /* padding-left: 10px; */
  margin: 20px 0 40px;
}
.form-control input {
  width: 100%;
  /* padding: 10px; */
  padding-bottom: 15px;
  border: 0;
  outline: none;
  background-color:  transparent;
  border-bottom: 2px solid white;
  display: block;
  width: 100%;
  /* margin-bottom: 30px; */
  padding: 15px 0;
  color: white;
  font-size: 18px;
  /* line-height: 1; */
}
.form-control input:focus,
.form-control input:valid { /* 输入框获得焦点或内容有效 */
  outline: none;
  border-bottom-color: skyblue;
}
.form-control label {
  top: 15px;
  position: absolute;
}
.form-control label span {
  display: inline-block;
  font-size: 18px;
  min-width: 5px;
  transform: 0.3 cubic-bezier(0.645, -0.045, 0.355, 1); /* 平滑过渡 */
  /* cubic-bezier(0.645, -0.045, 0.355, 1) 贝塞尔曲线 */
}
.form-control input:focus + label span,
.form-control input:valid + label span {
  transform: translateY(-15px) scale(0.75);
  color: skyblue;
}
.btn {
  cursor: pointer;
  display: inline-block;
  width: 100%;
  height: 40px;
  padding: 15px;
  font-size: 16px;
  border: 0;
  background-color: skyblue;
  border-radius: 5px;
  text-align: center;
}
.btn:focus {
  outline: none;

}
.bin:active {
  transform: scale(0.9);
}
.text {
  /* color: white; */
  margin-top: 30px;
}
.text a {
  color: skyblue;
  text-decoration: none;
}